The teaching Prophet Muhammed Pbuh. if it's not
found in the Quran then look for it in the Sunnah of Prophet Muhammed Pbuh
(Ahadith)
Here is a beautiful Hadith which clarifies this.
Harith ibn Amr reported: Some men among the
companions of Mu’adh said the Messenger of Allah, peace and blessings be upon
him, sent him to Yemen and the Prophet said:
كَيْفَ
تَقْضِي
How will you judge?
Mu’adh said, “I will judge according to what is in
the Book of Allah.”
The Prophet said:
فَإِنْ
لَمْ يَكُنْ فِي كِتَابِ اللَّهِ
What if it is not in the Book of Allah?
Mu’adh said, “Then with the tradition (sunnah) of
the Messenger of Allah.”
The Prophet said:
فَإِنْ
لَمْ يَكُنْ فِي سُنَّةِ رَسُولِ اللَّهِ
What if it is not in the tradition of the Messenger
of Allah?
Mu’adh said, “Then I will strive to form an opinion
(ijtihad).”
The Prophet said:
الْحَمْدُ
لِلَّهِ الَّذِي وَفَّقَ رَسُولَ رَسُولِ اللَّهِ
All praise is due to Allah who has made suitable
the messenger of the Messenger of Allah.
(Source: Sunan At-Tirmidhi 1327, Grade: Sahih)
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From this beautiful Hadith we gather that if
something is not found in the Quran then we should look for it in the Sunna of
Prophet Muhammed Pbuh. If it's not found both in the Quran and Sunna of Prophet
Pbuh then strive to form an opinion (ijtihad).
Next time a non-Muslim asks you show from the Quran
where is the word Tawheed mentioned. Do not hesitate to tell them as Muslims we
base our teachings from both Quran and Sunnah. Show them the Hadith which was
confirmed by Prophet Muhammed Pbuh.
We are not like the Christians who follow the bible
only. We Muslims follow both Quran and Sunnah.
Hudhaifa reported:
The Messenger of Allah (ﷺ) narrated to us two ahadith. I have seen one
(crystallized into reality), and I am waiting for the other. He told us:
Trustworthiness descended in the innermost (root) of the hearts of people. Then
the Qur'an was revealed and they learnt from the Qur'an and they learnt from
the Sunnah….. (Sahih Muslim Book 1, Hadith 274)
Yahya related to me from Malik that he heard that
the Messenger of Allah, may Allah bless him and grant him peace, said, "I
have left two matters with you. As long as you hold to them, you will not go
the wrong way. They are the Book of Allah and the Sunna of His Prophet."
(Muwatta Malik The Decree Book 46, Hadith 3)
Any Islamic matters in discussions both Quran and
Sunnah should be used. Thus, asking us where Tawheed is found we can show you
from the Sunnah of Prophet Muhammed Pbuh. You can't demand something which we
have to agree with.
Remember we are not to entertain the non Muslims.